Diamond has a number of properties which make it attractive for use as a coating for various materials. Among these properties are extreme hardness, inertness, and excellent transmissivity of certain radiation. Diamond is also an extraordinary heat conductor, thermally stable, and an electrical insulator.
In recent years, a number of techniques have been developed for depositing polycrystalline diamond film on surfaces of various substances. One preferred technique is chemical vapor deposition ("CVD"), for example plasma beam CVD or microwave plasma CVD, wherein plasmas of a hydrocarbon and hydrogen are used to grow diamond film.
For certain applications, it may be desirable to deposit synthetic diamond on various types of substrate materials. [As used herein, the term substrate is used generically, and can be any suitable material of any suitable shape.] Some substrate materials have a coefficient of thermal expansion that is relatively similar to that of synthetic diamond. When synthetic diamond is deposited at elevated temperature on such material, and then cools to room temperature, the relatively small difference in coefficient of thermal expansion between the diamond film and the substrate generally does not give rise to excessive stresses at the substrate/diamond interface upon cooling. However, if it is necessary or desirable to deposit synthetic diamond on a substrate having a coefficient of thermal expansion that is relatively dissimilar to that of diamond film (e.g. more than ten percent greater or less than the coefficient of thermal expansion of synthetic diamond), the stress on the diamond film that results from incremental displacement of the substrate upon cooling, can have deleterious effects, such as cracking of the diamond film.
It is among the objects of the present invention to prevent the described type of problem that can arise when depositing diamond film on a substrate having a coefficient of thermal expansion that is poorly matched to diamond.